JP2007168153A - Printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing method capable of suppressing induction of density variation when a gradation value of image data is corrected based on a correction value of the density. <P>SOLUTION: There is disclosed the printing method wherein by referring to correlationship information in which correlationship between gradation values of densities and formation rates of dots are regulated about the dots having different sizes, the formation rate of the dot corresponding to the gradation value of the density of image data is acquired, and the dot is formed on a medium according to the formation rate to print an image. The printing method comprises a step of judging whether or not the formation rate of the dot having a certain size in the plurality of sizes is changed from the positive value to zero by virtue of the correction when the correction of the gradation value of the image data is carried out based on the correction value of the regulated density, and a step of changing the correlatioship information based on the judgment result. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printing method for printing an image on a medium.

A so-called inkjet printer is one example of a printing apparatus that prints an image by forming dots of a plurality of sizes on a medium such as paper based on image data having density gradation values. At the time of printing, the density level of the image data is referred to by referring to a dot generation rate table (a correspondence relationship between gradation values and dot generation rates is defined for each dot size). A dot generation rate corresponding to the tone value is acquired, and the dot is formed on a medium based on the generation rate, and an image is printed (see Patent Document 1).
Japanese Patent Application Laid-Open No. 2005-224977

  By the way, in order to suppress the density unevenness of the image in such a printing apparatus, the gradation value of the area corresponding to the density unevenness is corrected on the image data. For example, for a printing apparatus that tends to print darker than the target density for a predetermined area on the medium, the predetermined value is previously set in correspondence with the predetermined area so that the gradation value corresponding to the predetermined area becomes smaller after correction. Set the correction value. Then, since the gradation value is corrected to be small by the correction value, the dot generation rate is accordingly reduced, and as a result, the density of the predetermined area on the medium is macroscopically lighter than before the correction. Thus, density unevenness is suppressed.

However, when this correction changes the generation rate of a dot of a certain size from a positive value to zero, the dot of the certain size is not formed at all in the predetermined area. Concerning the point, there is a possibility that the continuity with the surrounding area is remarkably lacked, and the predetermined area looks like density unevenness.
In other words, there is a possibility that density unevenness is induced despite the correction of the gradation value of the image data to suppress the density unevenness.

  The present invention has been made in view of such a problem, and an object of the present invention is to perform printing that can suppress the induction of density unevenness when correcting the gradation value of image data based on the correction value of density. To realize the method.

The main invention for solving the above problems is:
The dot generation rate corresponding to the density gradation value of the image data is obtained by referring to correspondence information that defines the correspondence between the density gradation value and the dot generation rate for dots of a plurality of sizes. A printing method for printing an image by forming the dots on a medium based on the generation rate,
When correcting the gradation value of the image data based on a predetermined density correction value, whether or not the generation rate of a dot of a certain size among the plurality of sizes is changed from a positive value to zero by the correction. A step of determining whether or not
And a step of changing the correspondence information based on a result of the determination.

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

The dot generation rate corresponding to the density gradation value of the image data is obtained by referring to correspondence information that defines the correspondence between the density gradation value and the dot generation rate for dots of a plurality of sizes. A printing method for printing an image by forming the dots on a medium based on the generation rate,
When correcting the gradation value of the image data based on a predetermined density correction value, whether or not the generation rate of a dot of a certain size among the plurality of sizes is changed from a positive value to zero by the correction. A step of determining whether or not
Changing the correspondence information based on a result of the determination. A printing method comprising:

According to such a printing method, when the generation rate of the dot of a certain size is changed from a positive value to zero by the correction, the correspondence information is changed. Therefore, by appropriately setting the correspondence relationship information in advance, it is possible to maintain the generation rate corresponding to the corrected gradation value at a positive value. That is, even after correction, the dots of a certain size are formed on the medium at a predetermined generation rate.
Accordingly, it is possible to prevent the dot of the certain size from being formed at all in the predetermined area on the medium on which the dot of the certain size is to be formed due to the correction. As a result, regarding the dot configuration, continuity with the surrounding area can be maintained, and the predetermined area can be effectively prevented from appearing as density unevenness.

In such a printing method,
The plurality of size dots are small dots, medium dots larger than the small dots, and large dots larger than the medium dots,
The correspondence information is preferably a dot generation rate table that defines the correspondence between the gradation value and the dot generation rate for each size.

  According to such a printing method, since an image can be printed using small, medium, and large dots, the range of printing expression can be expanded.

In such a printing method,
In the dot generation rate table,
In a range of gradation values greater than zero and less than or equal to the first gradation value, only the small dot generation rate is a positive value;
In the range of gradation values greater than the first gradation value and less than or equal to the second gradation value, only the generation rate of the small dots and the medium dots is a positive value;
In a range of gradation values larger than the second gradation value, it may be specified that the generation rate of the large dots is a positive value.

In such a printing method,
The dot of the certain size is preferably the medium dot.

  The first gradation value is normally included in a gradation value range of a so-called halftone area where density unevenness is easily visible. Therefore, when there is no medium dot by the correction, density unevenness due to the medium dot is easily visually recognized. However, according to the printing method, it is prevented that there is no medium dot with the correction. Therefore, continuity with the surrounding area can be maintained for the dot configuration points, and as a result, it is possible to effectively prevent the predetermined area from appearing as density unevenness.

In such a printing method,
As the dot generation rate table, an auxiliary dot generation rate used in place of the regular dot generation rate table when the determination result is zero, in addition to the regular dot generation rate table that is used regularly. A table is prepared,
In the auxiliary dot generation rate table, it is desirable that the first gradation value is set to a smaller value than in the case of the regular dot generation rate table.

According to such a printing method, the first tone value is set to be smaller in the auxiliary dot generation rate table than in the regular dot generation rate table. The first gradation value indicates the minimum gradation value at which the medium dot is to be generated.
Therefore, even if the medium dot generation rate in the normal dot generation rate table is changed from a positive value to zero by the correction, if the auxiliary dot generation rate table is used, the medium dot generation rate is set to a positive value. Can be maintained.
As a result, it is possible to effectively prevent the medium dot from being completely removed from the predetermined area on the medium due to the correction, and the configuration of the dot to be greatly different from the surrounding area. It can be effectively prevented that the predetermined area looks like density unevenness due to the correction.

In such a printing method,
The image is printed by repeating an ink ejection operation for ejecting ink from the nozzle while moving the nozzle in the movement direction, and a conveyance operation for conveying the medium in a conveyance direction that intersects the movement direction.
The gradation value of the image data is set for each unit region adjacent to the moving direction and adjacent to the transport direction,
The determination is preferably performed for each unit region.
According to such a printing method, since the determination is performed for each unit area, the dot of the certain size is generated in the predetermined area on the medium on which the dot of the certain size is to be formed according to the correction. It can be more effectively prevented that it is not formed at all.

In such a printing method,
The image is divided with respect to the transport direction in row area units composed of a plurality of the unit areas adjacent in the moving direction,
It is desirable that the correction value is set for each row region.
According to such a printing method, since the correction value is set for each row region, density unevenness can be more reliably suppressed.

In such a printing method,
The correction value is preferably set based on a density reading value read for each row region from a test pattern printed at a predetermined density.
According to such a printing method, the correction value for each row region is set based on the read value of the density read for each row region from the test pattern printed at a predetermined density. It is possible to effectively suppress density unevenness that may occur in units of regions.

In such a printing method,
When the generation rate is α% in a plurality of unit regions, the dots may be formed in α% unit regions of the plurality of unit regions.

In such a printing method,
The image is composed of a plurality of color dots,
The image data has the gradation value for each color,
The correspondence information is prepared for each color,
Based on the correspondence information of the same color, it may be regulated so that two or more dots are not overlapped in the same unit area.

In addition, by referring to correspondence information that defines the correspondence between density gradation values and dot generation rates for dots of a plurality of sizes, the dot generation rate corresponding to the density gradation values of image data can be determined. A printing method for obtaining and printing an image by forming the dots on a medium based on the generation rate,
When correcting the gradation value of the image data based on a predetermined density correction value, whether or not the generation rate of a dot of a certain size among the plurality of sizes is changed from a positive value to zero by the correction. A step of determining whether or not
Changing the correspondence information based on the result of the determination, and
The plurality of size dots are small dots, medium dots larger than the small dots, and large dots larger than the medium dots, and the correspondence information includes the gradation value and the dot generation rate. It is a dot generation rate table that defines the correspondence for each size,
In the dot generation rate table, in the range of gradation values greater than zero and less than or equal to the first gradation value, only the small dot generation rate is positive and greater than the first gradation value. In the range of gradation values equal to or lower than the second gradation value, only the generation rate of the small dots and the medium dots is positive, and in the range of gradation values larger than the second gradation value, It is specified that the generation rate of large dots is a positive value,
The dot of the certain size is the medium dot,
As the dot generation rate table, an auxiliary dot generation rate used in place of the regular dot generation rate table when the determination result is zero, in addition to the regular dot generation rate table that is used regularly. A table is prepared, and in the auxiliary dot generation rate table, the first gradation value is set to a smaller value than in the case of the regular dot generation rate table,
The image is printed by repeating an ink ejection operation for ejecting ink from the nozzle while moving the nozzle in the movement direction, and a conveyance operation for conveying the medium in a conveyance direction that intersects the movement direction. The gradation value of data is set for each unit region adjacent to the moving direction and adjacent to the transport direction, and the determination is performed for each unit region.
The image is divided in a row region unit composed of a plurality of unit regions adjacent in the moving direction, and is divided with respect to the transport direction, and the correction value is set for each row region,
The correction value is set based on a density reading value read for each row region from a test pattern printed at a predetermined density,
When the generation rate is α% in a plurality of unit regions, the dots are formed for α% unit regions of the plurality of unit regions,
The image is composed of dots of a plurality of colors, the image data has the gradation value for each color, the correspondence information is prepared for each color, and is based on the correspondence information of the same color The printing method is characterized in that two or more dots are not overlapped in the same unit area.
According to such a printing method, since all the effects described above are exhibited, the object of the present invention can be achieved more effectively.

=== About Overall Configuration of Printing System 100 ===
FIG. 1 is an explanatory diagram of the overall configuration of the printing system 100. The printing system is a system including at least a printing apparatus and a printing control apparatus that controls the operation of the printing apparatus. Here, the printing system 100 includes a printer 1, a computer 110, a display device 120, an input device 130, a recording / reproducing device 140, and a scanner 150.

  The printer 1 prints an image on a medium such as paper, cloth, film, or OHP paper. The computer 110 is communicably connected to the printer 1 and outputs print data corresponding to the image to the printer 1 in order to cause the printer 1 to print an image. Computer programs such as application programs and printer drivers are installed in the computer 110. Further, the computer 110 is installed with a scanner driver for controlling the scanner 150 and receiving image data of the original 5 read by the scanner 150.

=== About Printer 1 ===
<Overall Configuration of Printer 1>
FIG. 2 is a block diagram of the overall configuration of the printer 1. 3A is a schematic diagram of the overall configuration of the printer 1, and FIG. 3B is a cross-sectional view of the overall configuration of the printer 1.

  The printer 1 includes a transport unit 20, a carriage unit 30, a head unit 40, a detector group 50, and a controller 60. The printer 1 that has received print data from the computer 110, which is an external device, controls each unit (the conveyance unit 20, the carriage unit 30, and the head unit 40) by the controller 60. The controller 60 controls each unit based on the print data received from the computer 110 and prints an image on paper. The situation in the printer 1 is monitored by a detector group 50, and the detector group 50 outputs a detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

<About the transport unit 20>
The transport unit 20 transports a medium such as paper in a predetermined direction (hereinafter referred to as a transport direction). The transport unit 20 includes a paper feed roller 21, a transport motor 22, a transport roller 23, a platen 24, and a paper discharge roller 25. The paper feed roller 21 is a roller for feeding the paper inserted into the paper insertion slot into the printer 1. The transport roller 23 is a roller that transports the paper fed by the paper feed roller 21 to a printable area, and is driven by the transport motor 22. The platen 24 supports the paper being printed. The paper discharge roller 25 is a roller for discharging paper to the outside of the printer 1 and is provided on the downstream side in the transport direction with respect to the printable area. The paper discharge roller 25 rotates in synchronization with the transport roller 23.

<About the carriage unit 30>
The carriage unit 30 is for moving a later-described head 41 in a predetermined direction (hereinafter referred to as a moving direction). The carriage unit 30 includes a carriage 31 and a carriage motor 32. The carriage 31 can reciprocate in the moving direction. Further, the carriage 31 detachably holds an ink cartridge that stores ink. The carriage motor 32 is a motor for moving the carriage 31 in the movement direction.

<About the head unit 40>
The head unit 40 is for ejecting ink onto paper. The head unit 40 has a head 41. The head 41 has a plurality of nozzles, and ejects ink intermittently from each nozzle. The head 41 is provided on the carriage 31. Therefore, when the carriage 31 moves in the movement direction, the head 41 also moves in the movement direction. Then, by intermittently ejecting ink while the head 41 is moving in the moving direction, a dot row along the moving direction is formed on the paper.

  FIG. 4A is an explanatory diagram of the arrangement of nozzles on the lower surface of the head 41. On the lower surface of the head 41, a black ink nozzle group K, a cyan ink nozzle group C, a magenta ink nozzle group M, and a yellow ink nozzle group Y are formed. Each nozzle group includes a plurality of nozzles for ejecting ink of each color. The plurality of nozzles of each nozzle group are aligned at a constant interval (nozzle pitch: k · D) along the transport direction. Here, D is the minimum dot pitch in the carrying direction (that is, the interval at the highest resolution of dots formed on the paper). K is an integer of 1 or more. For example, when the nozzle pitch is 180 dpi (1/180 inch) and the dot pitch in the transport direction is 720 dpi (1/720 inch), k = 4. The nozzles of each nozzle group are assigned a smaller number as the nozzles on the downstream side (# 1 to # 180). Each nozzle is provided with an ink chamber (not shown) and a piezo element (not shown). The ink chamber is expanded and contracted by driving the piezo element, and ink droplets are ejected from the nozzle.

  FIG. 4B is an explanatory diagram of a drive circuit 220 for driving the piezo element. The drive circuit 220 is provided in the unit control circuit 64 included in the controller 60 described above, and includes an original drive signal generator 221 and a plurality of mask circuits 222 as shown in FIG. Here, this drive circuit 220 is provided for each nozzle group, and the piezo elements are individually driven for each nozzle group.

  The original drive signal generator 221 generates an original drive signal ODRV that is used in common by the nozzles # 1 to # 180. This original drive signal ODRV is supplied with two pulses, a first pulse W1 and a second pulse W2, within a period of one pixel (within a time during which the carriage 31 crosses the interval of one pixel), as shown in the lower part of the figure. It is a signal that contains. The original drive signal ODRV generated by the original drive signal generator 221 is output to each mask circuit 222.

  The mask circuit 222 is provided corresponding to a plurality of piezoelectric elements that drive the nozzles # 1 to # 180 of the head 41, respectively. Each mask circuit 222 receives the original drive signal ODRV from the original drive signal generator 221 and the print signal PRT (i). The print signal PRT (i) is pixel data corresponding to a pixel included in the print data, and is a binary signal having 2-bit information for one pixel. Each bit corresponds to the first pulse W1 and the second pulse W2, respectively. The mask circuit 222 is a gate for blocking or passing the original drive signal ODRV in accordance with the level of the print signal PRT (i). That is, when the print signal PRT (i) is at level “0”, the pulse of the original drive signal ODRV is cut off, while when the print signal PRT (i) is at level “1”, the corresponding pulse of the original drive signal ODRV is output. It passes as it is and is output as an actual drive signal DRV toward the piezoelectric elements of the nozzles # 1 to # 180. Each piezo element is driven based on the actual drive signal DRV from the mask circuit 222 to eject ink.

  FIG. 4C is a timing chart of the original drive signal ODRV, the print signal PRT (i), and the actual drive signal DRV (i) showing the operation of the original drive signal generator 221. As shown in the figure, the original drive signal ODRV sequentially generates a first pulse W1 and a second pulse W2 in each pixel section T1, T2, T3, T4. Note that the pixel section has the same meaning as the movement section of the carriage 41 for one pixel.

  Here, when the print signal PRT (i) corresponds to 2-bit pixel data “10”, only the first pulse W1 is output in the first half of one pixel interval. As a result, small-sized ink droplets are ejected from the nozzles, and small dots are formed on the paper. When the print signal PRT (i) corresponds to 2-bit pixel data “01”, only the second pulse W2 is output in the second half of one pixel interval. As a result, medium-sized ink droplets are ejected from the nozzles, and medium dots are formed on the paper. When the print signal PRT (i) corresponds to the 2-bit pixel data “11”, the first pulse W1 and the second pulse W2 are output in one pixel section. As a result, medium-sized ink droplets and small-sized ink droplets are continuously ejected from the nozzles, and medium dots and small dots are merged to form large dots on the paper.

  As described above, the actual drive signal DRV (i) in one pixel section is shaped to have three different waveforms according to three different values of the print signal PRT (i), and is based on these signals. The head 41 can form dots of three types of sizes and can adjust the amount of ink ejected in the pixel section. Needless to say, when the print signal PRT (i) corresponds to the 2-bit pixel data “00” as in the pixel section T4, no ink droplets are ejected from the nozzles and no dots are formed on the paper. Yes.

<Regarding the detector group 50>
The detector group 50 includes a linear encoder 51, a rotary encoder 52, a paper detection sensor 53, an optical sensor 54, and the like. The linear encoder 51 is for detecting the position of the carriage 31 in the moving direction. The rotary encoder 52 is for detecting the rotation amount of the transport roller 23. The paper detection sensor 53 is for detecting the position of the leading edge of the paper to be printed. The optical sensor 54 is attached to the carriage 31. The optical sensor 54 detects the presence or absence of paper by the light receiving unit detecting reflected light of light irradiated on the paper from the light emitting unit.

<About the controller 60>
The controller 60 is a control unit for controlling the printer 1. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64. The interface unit 61 is for transmitting and receiving data between the computer 110 which is an external device and the printer 1. The CPU 62 is an arithmetic processing unit for controlling the entire printer 1. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and includes storage elements such as a RAM and an EEPROM. The CPU 62 controls each unit via the unit control circuit 64 in accordance with a program stored in the memory 63.

=== Scanner 150 ===
FIG. 5A is a longitudinal sectional view of the scanner 150. FIG. 5B is a top view of the scanner 150 with the upper lid 151 removed.

  The scanner 150 includes an upper cover 151, a document table glass 152 on which the document 5 is placed, a reading carriage 153 that moves in the sub-scanning direction while facing the document 5 through the document table glass 152, and a sub-scanning of the reading carriage 153. A guide member 154 for guiding in a direction, a moving mechanism 155 for moving the reading carriage 153, and a scanner controller (not shown) for controlling each part in the scanner 150 are provided. The reading carriage 153 receives an exposure lamp 157 for irradiating the original 5 with light, a line sensor 158 for detecting an image of a line in the main scanning direction (direction perpendicular to the paper surface in FIG. 5A), and reflected light from the original 5. An optical system 159 for guiding to the line sensor 158 is provided. The dotted line inside the reading carriage 153 in the drawing indicates the locus of light.

  When reading the image of the document 5, the operator opens the upper cover 151, places the document 5 on the document table glass 152, and closes the upper cover 151. Then, the scanner controller moves the reading carriage 153 along the sub-scanning direction with the exposure lamp 157 emitting light, and reads the image on the surface of the document 5 by the line sensor 158. The scanner controller transmits the read image data to the scanner driver of the computer 110, whereby the computer 110 acquires the image data of the document 5.

=== Print processing ===
<About print processing>
FIG. 6 is a flowchart of the operation during printing. Each operation described below is executed by the controller 60 controlling each unit in accordance with a program stored in the memory 63. This program has code for executing each operation.

  Print command reception (S001): First, the controller 60 receives a print command from the computer 110 via the interface unit 61. This print command is included in the header of print data transmitted from the computer 110. Then, the controller 60 analyzes the contents of various commands included in the received print data, and performs the following paper feeding operation / conveying operation / dot forming operation using each unit.

  Paper Feed Operation (S002): The paper feed operation is an operation for supplying paper to be printed into the printer 1 and positioning the paper at a predetermined position (also referred to as a cueing position) where printing is possible. The controller 60 rotates the paper feed roller 21 and the transport roller 23 to position the paper at the cueing position.

  Dot Forming Operation (S003): The dot forming operation is an operation for intermittently ejecting ink from the head 41 moving in the moving direction to form dots on the paper. The controller 60 drives the carriage motor 32 to move the carriage 31 in the movement direction, and ejects ink from the head 41 based on the pixel data included in the print data while the carriage 31 is moving. When ink droplets ejected from the head 41 land on the paper, dots are formed on the paper. Since ink is intermittently ejected from the moving head 41, a dot row composed of a plurality of dots along the moving direction is formed on the paper.

  Transport Operation (S004): The transport operation is an operation of moving the paper relative to the head 41 along the transport direction. The controller 60 rotates the transport roller 23 to transport the paper in the transport direction perpendicular to the moving direction. With this carrying operation, the head 41 can form dots at the next dot forming operation at a position different from the position of the dots formed by the previous dot forming operation.

  Paper discharge determination (S005): The controller 60 determines whether or not to discharge the paper being printed. That is, if there is still data to be printed on the paper being printed, no paper is discharged. The controller 60 alternately repeats the dot formation operation and the transport operation until there is no more data to be printed, and gradually prints an image composed of dots on paper.

  Paper Discharge Operation (S006): When there is no more data to be printed on the paper being printed, the controller 60 discharges the paper by rotating the paper discharge roller 25. The determination of whether or not to discharge paper may be based on a paper discharge command included in the print data.

  Print end determination (S007): Next, the controller 60 determines whether or not to continue printing. If printing is to be performed on the next paper, printing is continued and the next paper feeding operation is started. If printing is not performed on the next paper, the printing operation is terminated.

<Dot row formation>
First, normal printing will be described. Normal printing is performed by a printing method called interlaced printing. Here, “interlaced printing” means printing in which non-recorded dot rows are sandwiched between dot rows recorded in one pass. “Pass” refers to a dot formation operation, and “pass n” refers to the nth dot formation operation. A “dot row” is a row of dots arranged in the moving direction.

  7A and 7B are explanatory diagrams of normal printing. 7A shows the position of the head 41 and how dots are formed in pass n to pass n + 3, and FIG. 7B shows the position of the head 41 and how dots are formed in pass n to pass n + 4.

  7A and 7B, for convenience of explanation, only one nozzle group is shown instead of the head 41, and the number of nozzles in the nozzle group is also reduced. Although the nozzle group is depicted as moving with respect to the paper, this figure shows the relative position between the nozzle group (head 41) and the paper. It is moved in the transport direction. Also, for convenience of explanation, each nozzle is shown as having only a few dots (circles in the figure), but in reality, ink droplets are ejected intermittently from nozzles that move in the direction of movement. Therefore, a large number of dots are arranged in the moving direction to form a dot row. Of course, the dot may not be formed depending on the pixel data.

  In the figure, nozzles indicated by black circles are nozzles that can eject ink, and nozzles indicated by white circles are nozzles that cannot eject ink. Further, in the figure, the dot indicated by a black circle is a dot formed in the last pass, and the dot indicated by a white circle is a dot formed in the previous pass.

  In this interlaced printing, each time the paper is transported at a constant transport amount F in the transport direction, each nozzle records a dot row immediately above the dot row recorded in the immediately preceding pass. In order to perform recording with a constant carry amount in this way, (1) the number N (integer) of nozzles that can eject ink is relatively prime to k, and (2) the carry amount F is N · The condition is that it is set to D. Here, N = 7, k = 4, F = 7 · D (D = 1/720 inch).

  However, there are places where dot rows cannot be formed continuously in the transport direction only by this normal printing. Therefore, printing methods called leading edge printing and trailing edge printing are performed before and after normal printing.

  FIG. 8 is an explanatory diagram of leading edge printing and trailing edge printing. The first five passes are leading edge printing, and the last five passes are trailing edge printing.

  In front-end printing, when the vicinity of the front end of a print image is printed, the paper is transported by a transport amount (1 · D or 2 · D) smaller than the transport amount (7 · D) during normal printing. In front-end printing, the nozzles that eject ink are not constant. In the trailing edge printing, as in the leading edge printing, when the vicinity of the trailing edge of the image is printed, the transportation amount (1 · D or 2 · D) is smaller than the transportation amount (7 · D) during normal printing. The paper is conveyed. Further, in the rear end printing, the nozzles that eject ink are not constant, as in the front end printing. Thereby, a plurality of dot rows that are continuously arranged in the transport direction can be formed between the first dot row and the last dot row.

  An area (intermediate area) in which a dot row is formed only by normal printing is called a “normal printing area”. In addition, a region (downstream end region) located on the front end side (downstream in the transport direction) of the paper with respect to the normal print region is referred to as a “leading end print region”. Further, a region (upstream end region) located on the rear end side (upstream side in the transport direction) from the normal print region is referred to as a “rear end print region”. Thirty dot rows are formed in the leading edge printing area. Similarly, 30 dot rows are also formed in the trailing edge print region. On the other hand, in the normal printing area, although it depends on the size of the paper, approximately several thousand dot rows are formed.

  The arrangement of the nozzles assigned to each row region of the normal print region (refers to a region where a dot row is to be formed and the details of the definition and the like will be described later) is a predetermined number P corresponding to the carry amount (here There are regularities in each of the 7) row regions. That is, the arrangement of the nozzles assigned to the row region changes with seven row regions as one cycle.

  For example, the first to seventh row regions of the normal print region in FIG. 8 are respectively represented by nozzle # 3, nozzle # 5, nozzle # 7, nozzle # 2, nozzle # 4, nozzle # 6, and nozzle # 8. A dot row is formed, and dot rows are also formed in the next eight and subsequent seven row regions by the nozzles in the same order.

  On the other hand, it is difficult to find regularity in the arrangement of nozzles assigned to each row area of the leading edge printing area and the trailing edge printing area as compared with the dot line of the normal printing area. However, the nozzles assigned to the respective row regions of the front end print region and the rear end print region are also determined in advance corresponding to each row region. For example, each time the leading edge printing is performed, as shown in FIG. 8, dot rows are formed by the nozzle # 2 in the first to fourth row regions in the leading edge printing region, and the nozzles are formed in the fifth row region. In # 3, a dot row is formed by nozzle # 2 in the sixth row region, nozzle # 3 in the seventh and eighth row regions, and nozzle # 4 in the ninth row region (hereinafter omitted). ) The arrangement of the nozzles does not change every time the leading edge printing is executed.

=== Correction of density unevenness ===
<About density unevenness (banding)>
Here, for the sake of simplification of description, the cause of density unevenness occurring in an image printed in a single color will be described. In the case of multicolor printing, the cause of density unevenness described below occurs for each color.

  FIG. 9A is an explanatory diagram of a state when dots are ideally formed. While the carriage 31 moves in the moving direction, ink is ejected from each nozzle, and ink is landed on the paper to form dots. Since each nozzle intermittently ejects ink during movement, a row of dots (dot row) is formed along the movement direction. Each dot row forms a long and narrow image piece along the moving direction, and a large number of image pieces are arranged in the carrying direction to form a printed image. Here, for simplification of explanation, it is assumed that an image having a constant density such that the dot generation rate is 50% is printed, and that the dot size is one kind.

  In the figure, since dots are ideally formed, each dot is accurately formed in a unit region defined on the paper, and a dot row is accurately formed in the row region.

  Here, the “unit area” refers to a virtually defined rectangular area on a medium such as paper, and is an area corresponding to a pixel that is a minimum structural unit of an image. The size and shape are determined according to the print resolution. For example, when the printing resolution is 720 dpi (moving direction) × 720 dpi (conveying direction), the unit area has a square shape with a size of about 35.28 μm × 35.28 μm (≈ 1/720 inch × 1/720 inch). Become an area. When the print resolution is 360 dpi × 720 dpi, the unit area is a rectangular area having a size of about 70.56 μm × 35.28 μm (≈ 1/360 inch × 1/720 inch). When an ink droplet is ideally ejected, the ink droplet lands at the center position of the unit region, and then the ink droplet spreads on the medium to form a dot in the unit region.

  Further, “row region” refers to a region composed of a plurality of unit regions arranged in the movement direction, and in the drawing, “row region” is shown as a region sandwiched between dotted lines. For example, when the printing resolution is 720 dpi × 720 dpi, the row region is a band-like region having a width of 30.28 μm (≈ 1/720 inch) in the transport direction. When ink droplets are ideally ejected intermittently from the nozzle moving in the moving direction, a dot row is formed in this row region, whereby each row region has a plurality of densities according to the coloration of that region. An image piece composed of the pixels is formed.

  FIG. 9B is an explanatory diagram of the influence of variations in nozzle processing accuracy. Here, due to variations in the flight direction of the ink droplets ejected from the nozzles, the dot row formed in the second row region is formed closer to the third row region side (upstream side in the transport direction). Further, the amount of ink droplets ejected toward the fifth row region is small, and the dots formed in the fifth row region are small.

  Although the image pieces having the same density should be formed in each row area originally, the image pieces are shaded according to the row areas due to variations in processing accuracy. For example, the image piece in the second row region is relatively light and the image piece in the third row region is relatively dark. Further, the image piece in the fifth row region becomes relatively light.

  When the print image composed of such dot rows is viewed macroscopically, striped density unevenness along the moving direction of the carriage 31 is visually recognized. This density unevenness causes a reduction in image quality of the printed image.

  FIG. 9C is an explanatory diagram of a state when dots are formed using a printing method for suppressing such density unevenness. Here, the gradation value of pixel data (CMYK pixel data described later) of the pixel corresponding to the row region is corrected so that a dark image piece is formed in a row region that is dark and easily visible. Further, the gradation value of the pixel data of the pixel corresponding to the row region is corrected so that a dark image piece is formed in a row region that is easily viewed. For example, the dot generation rate of the second row region in the figure is increased, the dot generation rate of the third row region is decreased, and the dot generation rate of the fifth row region is increased. The gradation value of the pixel data of the pixel corresponding to the column area is corrected. Thereby, the dot generation rate of the dot row in each row region is changed, the density of the image pieces in the row region is corrected, and the density unevenness of the entire print image is suppressed.

  By the way, in FIG. 9B, the reason why the density of the image piece formed in the third row region is high is not due to the influence of the nozzle forming the dot row in the third row region, but the adjacent second row. This is due to the influence of nozzles that form dot rows in the region. For this reason, when a nozzle that forms a dot row in the third row region forms a dot row in another row region, an image piece formed in that row region is not always dark. That is, even if the image pieces are formed by the same nozzle, the density may be different if the nozzles that form adjacent image pieces are different. In such a case, the density unevenness cannot be suppressed with the correction value simply associated with the nozzle. Therefore, in the printer 1, the gradation value of the pixel data is corrected based on the correction value set for each row area.

  For this purpose, in the printer manufacturing factory, the printer 1 prints a correction pattern, the correction pattern is read by the scanner 150, and a correction value corresponding to each column region is calculated based on the density of each column region in the correction pattern. Store in the memory of the printer 1. The correction value stored in the printer 1 reflects the density unevenness characteristics of each printer 1.

  Then, under the user who purchased the printer 1, the printer driver reads the correction value from the printer 1, corrects the gradation value of the pixel data based on the correction value, and print data based on the corrected gradation value. And the printer 1 performs printing based on the print data.

<About processing at printer manufacturing plants>
FIG. 10 is a flowchart of a correction value setting process performed after the printer 1 is manufactured. First, the worker connects the printer 1 to be processed to the computer 110 in the factory (S101). The computer 110 in the factory is also connected to the scanner 150, and in advance, a printer driver for causing the printer 1 to print a test pattern, a scanner driver for controlling the scanner 150, and a correction read from the scanner 150. A correction value setting program for performing image processing, analysis, etc. on the image data of the pattern for use is installed.

Next, the printer driver of the computer 110 causes the printer 1 to print a test pattern (S102).
FIG. 11 is an explanatory diagram of a test pattern, and FIG. 12 is an explanatory diagram of a correction pattern included in the test pattern. This test pattern is printed at a print resolution of 720 × 720 dpi, for example, and has four correction patterns for each color. Each correction pattern is composed of a band-shaped pattern of five types of density, an upper ruled line, a lower ruled line, a left ruled line, and a right ruled line.

  Each of the belt-like patterns is generated from image data having a constant gradation value in the conveyance direction, and gradation values 76 (density 30%), 102 (density 40%), 128 (density 50%), 153 (density 60%), and 179 (density 70%), which are patterns of dark density in order. These five types of gradation values (density) are referred to as “command gradation values (command density)” and are represented by symbols Sa (= 76), Sb (= 102), Sc (= 128), Sd (= 153) and Se (= 179).

  Since each belt-like pattern is formed by leading edge printing, normal printing, and trailing edge printing, it is composed of a leading edge printing region dot row, a normal printing region dot row, and a trailing edge printing region dot row. In normal printing, thousands of dot rows are formed in the normal printing region, but in printing the correction pattern, eight cycles of dot rows are formed in the normal printing region. Here, for the sake of simplification of explanation, it is assumed that the correction pattern is printed by printing in FIG. 8, and the belt-like pattern has 30 dot rows in the front end print area, 56 in the normal print area (= 7 (pieces / cycle). ) × 8 cycles) and a total of 116 dot rows including 30 dot rows in the trailing edge printing area. The upper ruled line is formed by the first dot row (dot row on the most downstream side in the transport direction) constituting the belt-like pattern. The lower ruled line is formed by the last dot row (dot row on the most upstream side in the transport direction) constituting the belt-like pattern.

  Incidentally, when printing this test pattern, it goes without saying that gradation value correction processing (see step S250 in FIG. 23) based on correction values described later is not performed.

  Next, the operator places the paper on which the test pattern is printed by the printer 1 on the platen glass 152 of the scanner 150, closes the upper lid 151, and sets the test pattern on the scanner 150. Then, the scanner driver of the computer 110 causes the scanner 150 to read the correction pattern (S103). Hereinafter, reading of a cyan correction pattern will be described. The correction patterns for other colors are read in the same manner.

  FIG. 13 is an explanatory diagram of the reading range of the cyan correction pattern. The range of the alternate long and short dash line surrounding the cyan correction pattern is the reading range when reading the cyan correction pattern. Parameters SX1, SY1, SW1, and SH1 for specifying this range are set in advance in the scanner driver by the correction value setting program. If the scanner 150 reads this range, the entire cyan correction pattern can be read even if the test pattern is set to the scanner 150 with a slight shift. By this processing, the image in the reading range in the figure is read by the computer 110 as rectangular image data having a reading resolution of 2880 × 2880 dpi.

  Next, the correction value setting program of the computer 110 detects the inclination θ of the correction pattern included in the image data (S104), and performs rotation processing corresponding to the inclination θ on the image data (S105).

FIG. 14A is an explanatory diagram of image data at the time of tilt detection. FIG. 14B is an explanatory diagram of detection of the position of the upper ruled line. FIG. 14C is an explanatory diagram of the image data after the rotation process. From the read image data, the correction value setting program includes KX1 pixel data from the left and KH pixel data from the top, and KX2 pixel data from the left and KH pixels from the top. Retrieve the data. The parameters KX1, KX2, and KH are determined in advance so that the pixels extracted at this time include the upper ruled line and do not include the right ruled line and the left ruled line. Then, the correction value setting program obtains the gravity center positions KY1 and KY2 of the gradation values of the extracted KH pixel data in order to detect the position of the upper ruled line. Then, the correction value setting program calculates the inclination θ of the correction pattern based on the parameters KX1 and KX2 and the barycentric positions KY1 and KY2, and rotates the image data based on the calculated inclination θ. Process.
θ = tan ⁻¹ {(KY2-KY1) / (KX2-KX1)}

  Next, the correction value setting program of the computer 110 trims unnecessary pixels from the image data (S106).

  FIG. 15A is an explanatory diagram of image data at the time of trimming. FIG. 15B is an explanatory diagram of a trimming position on the upper ruled line. Similar to the processing in step S104, the correction value setting program includes pixel data of KX1 pixels from the left, KH pixels from the top, and KX2 pixels from the left, from the rotated image data. Thus, pixel data of KH pixels are extracted from the top. Then, in order to detect the position of the upper ruled line, the correction value setting program obtains the gravity center positions KY1 and KY2 of the gradation values of the extracted KH pixel data, and calculates the average value of the two gravity center positions. Then, the nearest pixel boundary is determined as a trimming position at a position that is ½ the width of the row area from the center of gravity position. Here, since the resolution of the image data is 2880 dpi and the width of the row area is 720 dpi, ½ of the width of the row area corresponds to the width of two pixels. Then, the correction value setting program cuts out pixels above the determined trimming position and performs trimming.

  FIG. 15C is an explanatory diagram of the trimming position at the lower ruled line. As in the upper ruled line side, the correction value setting program includes KX1 pixel data from the left, KH pixel data from the bottom, and KX2 pixels from the left, among the rotated image data. Then, the pixel data of KH pixels are taken out from the bottom, and the center of gravity position of the lower ruled line is calculated. Then, the nearest pixel boundary is determined as the trimming position at a position that is ½ the width of the row area from the center of gravity position. Then, the correction value setting program cuts out pixels below the trimming position and performs trimming.

  Next, the correction value setting program of the computer 110 converts the resolution of the trimmed image data so that the number of pixels in the Y direction is 116 (the same number as the number of dot rows constituting the correction pattern) (S107). ).

  FIG. 16 is an explanatory diagram of resolution conversion. If the printer 1 ideally forms a correction pattern consisting of 116 dot rows of 720 dpi, and the scanner 150 ideally reads the correction pattern at 2880 dpi (4 times the resolution of the correction pattern), trimming is performed. The number of pixels in the Y direction of the subsequent image data should be 464 (= 116 × 4). However, in actuality, there are cases where the number of pixels in the Y direction of the image data does not become 464 due to the influence of misalignment during printing or reading. Here, the number of pixels in the Y direction of the image data after trimming is 470. The correction value setting program of the computer 110 uses the magnification of 116/470 (= [number of dot columns constituting the correction pattern] / [number of pixels in Y direction of image data after trimming]) for this image data. To perform resolution conversion (reduction processing). Here, the bicubic method is used for resolution conversion. As a result, the number of pixels in the Y direction of the image data after resolution conversion becomes 116. In other words, the image data of the correction pattern of 2880 dpi is converted into the image data of the correction pattern of 720 dpi. As a result, the number of pixels arranged in the Y direction and the number of column regions are the same, and the pixel columns and column regions in the X direction have a one-to-one correspondence. For example, the pixel column in the X direction positioned at the top corresponds to the first column region, and the pixel column positioned below corresponds to the second column region. In this resolution conversion, since the purpose is to set the number of pixels in the Y direction to 116, resolution conversion (reduction processing) in the X direction may not be performed.

  Next, the correction value setting program of the computer 110 measures the density of each of the five types of belt-like patterns in each row region (S108). Hereinafter, the measurement of the density of the left band-shaped pattern formed with the gradation value 76 (density 30%) in the first row region will be described. Measurements in other row regions are performed in the same manner. In addition, the measurement of the density of other band-like patterns is performed in the same manner.

  FIG. 17A is an explanatory diagram of image data when the left ruled line is detected. FIG. 17B is an explanatory diagram of detection of the position of the left ruled line. FIG. 17C is an explanatory diagram of the measurement range of the density of the band-like pattern having a density of 30% in the first row region. The correction value setting program extracts pixel data of HX pixels from the top and KX pixels from the left from the resolution-converted image data. The parameter KX is determined in advance so that the left ruled line is included in the pixels extracted at this time. Then, the correction value setting program obtains the barycentric position of the gradation value of the pixel data of the extracted KX pixels in order to detect the position of the left ruled line. It is known from the shape of the correction pattern that a strip-shaped pattern having a width of W3 and having a density of 30% exists on the right side by X2 from the position of the center of gravity (the position of the left ruled line). Therefore, the correction value setting program extracts pixel data in a dotted line range excluding the left and right W4 ranges of the belt-like pattern with reference to the barycentric position, and calculates an average value of gradation values of the pixel data in this range as 1 The measured value of the density in the second row region is 30%. Note that when measuring the density of a strip-like pattern having a density of 30% in the first row region, pixel data in a range one pixel below the dotted line range in the figure is extracted. In this way, the correction value setting program measures the density of the five types of belt-like patterns for each row region.

  FIG. 18 is a measurement value table summarizing the measurement results of the densities of the five types of cyan belt-like patterns. As described above, the correction value setting program of the computer 110 creates a measurement value table by associating the measurement values of the density of the five types of belt-like patterns for each row region. A measurement value table is also created for other colors. In the following description, the measured values of the band-shaped pattern of the gradation values Sa to Se are set to Ca to Ce for a certain row region, respectively.

  FIG. 19 is a graph of measured values of a band-like pattern having a cyan density of 30%, a density of 40%, and a density of 50%. Although each strip pattern is uniformly formed with gradation values Sa (= 76), Sb (= 102), and Sc (= 128), shading is generated for each row region. The density difference for each row area is a cause of density unevenness in the printed image.

  In order to eliminate the density unevenness, it is desirable that the measured value of each strip pattern is constant. Therefore, a process for making the measurement value of the belt-like pattern having the gradation value Sb (density 40%) constant will be considered. Here, the average value Cbt of the measurement values of all the row regions of the strip-like pattern having the gradation value Sb is determined as a target value of 40% density. In the row region j1 where the measurement value is lighter than the target value Cbt, in order for the density measurement value to approach the target value Cbt, it is considered that the gradation value should be corrected to be darker. On the other hand, in the row region j2 where the measured value is darker than the target value Cbt, in order for the measured value of density to approach the target Cbt, it is considered that the gradation value should be corrected to be lighter.

  Therefore, the correction value setting program of the computer 110 calculates a correction value corresponding to the row area (S109). Here, calculation of the correction value for the command gradation value Sb in a certain row region will be described. As will be described below, the correction value for the command gradation value Sb (density 40%) in the row region j1 in FIG. 19 is calculated based on the measured values of the gradation value Sb and the gradation value Sc (density 50%). Is done. On the other hand, the correction value for the command gradation value Sb (density 40%) of the row region j2 is calculated based on the measured values of the gradation value Sb and the gradation value Sa (density 30%).

FIG. 20A is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region j1. In this row region, the measured value Cb of the density of the strip pattern formed with the command tone value Sb shows a tone value smaller than the target value Cbt (in this row region, the average density of the strip pattern having a density of 30%. Paler). If the printer driver causes the printer 1 to form a density pattern of the target value Cbt in this row area, the command is based on the target command tone value Sbt calculated by the following equation (linear interpolation based on the straight line BC). do it.
Sbt = Sb + (Sc−Sb) × {(Cbt−Cb) / (Cc−Cb)}

FIG. 20B is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region j2. In this row area, the measured value Cb of the density of the strip pattern formed with the command tone value Sb shows a tone value larger than the target value Cbt (in this row area, the average density of the strip pattern having a density of 30%. Paler). If the printer driver causes the printer 1 to form a density pattern of the target value Cbt in this row region, the command is based on the target command tone value Sbt calculated by the following equation (linear interpolation based on the straight line AB). do it.
Sbt = Sb− (Sb−Sa) × {(Cbt−Cb) / (Ca−Cb)}

After calculating the target command tone value Sbt in this way, the correction value setting program calculates a correction value Hb for the command tone value Sb in this row region by the following equation.
Hb = (Sbt−Sb) / Sb

  The correction value setting program of the computer 110 calculates a correction value Hb for the gradation value Sb (density 40%) for each row region. Similarly, the correction value setting program sets the correction value Hc for the gradation value Sc (density 50%), the measurement value Cc for each row region, the measurement value Cb or Cd, and the command gradation value Sb or Sd. Based on the above, calculation is performed for each row region. Similarly, the correction value setting program sets the correction value Hd for the gradation value Sd (density 60%), the measurement value Cd of each row region, the measurement value Cc or Ce, and the command gradation value Sc or Se. Based on the above, calculation is performed for each row region. For other colors, three correction values (Hb, Hc, Hd) are calculated for each row region.

  By the way, as shown in FIG. 12, there are 56 row areas in the normal print area. As described above, the arrangement of the nozzles assigned to these row areas is 7 cycles as one period. Change. That is, as shown in FIG. 8, nozzle # 3, nozzle # 5, nozzle # 7, nozzle # 2, nozzle # 4, nozzle # 6, nozzle # 3 are arranged in the first to seventh row areas of the normal printing area, respectively. Dot rows are formed by the nozzle # 8, and dot rows are also formed by the nozzles in the same order in the next eight and subsequent seven row regions. Therefore, this regularity is taken into account in the calculation of the correction value for the normal printing area shown in FIG.

When the correction value setting program calculates the correction value in the first row area of the normal printing area (the 31st row area of the entire printing area), the above-described measurement value Ca is the nozzle # 3 in the normal printing area. The average value Ca _ave of the measured values of the 30% density of the first, eighth, fifteen, twenty-second, twenty-ninth, thirty-six, forty-third, and fifty eighth row regions is used. Similarly, when calculating a correction value in the first row region of the normal print region (the 31st row region of the entire print region), nozzle # 3 is assigned to the above-described measurement values Cb to Ce in the normal print region. The average values Cb _{ave to} Ce _ave of the measured values of the respective densities of the first, eighth, fifteenth, twenty-second, twenty-ninth, thirty-sixth, thirty-fourth, and fifty eighth row regions are used. Then, as described above, the correction values (Hb, Hc, Hd) for the first row area of the normal printing area are calculated based on the average values Ca _{ave to} Ce _ave instead of the above-described measured values Ca to Ce. The As described above, the correction value of the row region of the normal print region is calculated based on the average value of the measured values of the respective densities of every eighth row region. As a result, in the normal print region, correction values are calculated only for the first to seventh row regions, and correction values are not calculated for the eighth to 56th row regions. In other words, the correction values for the first to seventh seven row regions of the normal print region also become correction values for the eighth to 56th row regions.

Next, the correction value setting program of the computer 110 stores the correction value in the memory 63 of the printer 1 (S110).
FIG. 21 is an explanatory diagram of a cyan correction value table. There are three types of correction value tables for the leading edge printing area, the normal printing area, and the trailing edge printing area. In each correction value table, three correction values (Hb, Hc, Hd) are associated with each row region. For example, three correction values (Hb_n, Hc_n, Hd_n) are associated with the nth dot row in each row region. The three correction values (Hb_n, Hc_n, Hd_n) correspond to the command gradation values Sb (= 102), Sc (= 128), and Sd (= 153), respectively. The same applies to correction value tables for other colors.
After the correction value is stored in the memory 63 of the printer 1 in this way, the correction value setting process ends. Then, the printer 1 and the computer 110 are disconnected, and the printer 1 is also bundled with a CD-ROM storing a printer driver.

<About processing under the user>
FIG. 22 is a flowchart of processing performed under the user.
The user who purchased the printer 1 connects the printer 1 to the computer 110 owned by the user (of course, a computer different from the computer at the printer manufacturing factory) (S201, S301). Note that the scanner 150 may not be connected to the user's computer 110.

  Next, the user sets the enclosed CD-ROM in the recording / reproducing apparatus 140 and installs the printer driver (S202). The printer driver installed in the computer 110 requests the computer 110 to transmit correction values to the printer 1 (S203). In response to this request, the printer 1 transmits the correction value table stored in the memory 63 to the computer 110 (S302). The printer driver stores the correction value sent from the printer 1 in the memory (S204). Thereby, a correction value table is created on the computer side. After completing the processing so far, the printer driver enters a standby state until a print command is received from the user (NO in S205).

  Upon receiving a print command from the user (YES in S205), the printer driver generates print data based on the correction value (S206) and transmits the print data to the printer 1. The printer 1 performs a printing process according to the print data (S303).

FIG. 23 is a flowchart of print data generation processing. These processes are performed by the printer driver.
First, the printer driver performs resolution conversion processing (S210). The resolution conversion process is a process for converting image data (text data, image data, etc.) output from an application program into a resolution for printing on paper. For example, when the resolution when printing an image on paper is specified as 720 × 720 dpi, the image data received from the application program is converted into image data having a resolution of 720 × 720 dpi.

  The image data after the resolution conversion processing is composed of a large number of pixel data set for each pixel corresponding to the resolution, and each pixel data has 256 gradations represented by the RGB color space. Data (hereinafter referred to as RGB pixel data). Therefore, hereinafter, this image data is referred to as RGB image data.

  Next, the printer driver performs color conversion processing (S230). In the color conversion process, each RGB pixel data of the RGB image data is referred to as pixel data (hereinafter referred to as CMYK pixel data) of multi-level (for example, 256 levels) gradation values represented by a CMYK color space corresponding to the ink color. ). This color conversion processing is performed by the printer driver referring to a color conversion lookup table LUT in which the gradation values of RGB pixel data and the gradation values of CMYK pixel data are associated with each other. Hereinafter, the image data after the color conversion process is referred to as CMYK image data.

  Incidentally, this CMYK image data can be divided into C image data related to cyan (C), M image data related to magenta (M), Y image data related to yellow (Y), and K image data related to black (K). Further, the C, M, Y, and K image data are respectively C pixel data having a gradation value of cyan (C), M pixel data having a gradation value of magenta (M), and yellow. Y pixel data having a gradation value of (Y) density and K pixel data having a gradation value of black (K) density. Therefore, the above-described CMYK pixel data can be said to be pixel data configured by combining C pixel data, M pixel data, Y pixel data, and K pixel data.

  The C, M, Y, and K image data basically differ from each other only in terms of ink color, and have the same data structure. Therefore, when the contents are common in the following description, C image data relating to cyan (C) will be described as a representative of C, M, Y, K image data.

  Next, the printer driver performs gradation value correction processing (S250). The gradation value correction process is a process for correcting the gradation value of each pixel data of the CMYK image data based on the correction value corresponding to the column region to which the pixel data belongs. Since this process is applicable to any of C, M, Y, and K image data, only the process of C image data relating to cyan (C) will be described below.

  FIG. 24 is an explanatory diagram of the tone value correction process for the nth row region of cyan (C). This figure shows how the tone value S_in of the C pixel data of the pixels belonging to the nth row region of cyan is corrected. Note that the corrected gradation value is S_out.

  If the gradation value S_in of the C pixel data before correction is the same as the command gradation value Sb, the printer driver corrects the gradation value S_in to the target instruction gradation value Sbt, and the correspondence of the C pixel data. An image with the target density Cbt can be formed in the unit area. That is, if the tone value S_in of the C pixel data before correction is the same as the command tone value Sb, the tone value S_in (= Sb) is set to Sb using the correction value Hb corresponding to the command tone value Sb. It is good to correct to x (1 + Hb). Similarly, if the gradation value S of the C pixel data before correction is the same as the command gradation value Sc, the gradation value S_in (= Sc) should be corrected to Sc × (1 + Hc).

  On the other hand, when the gradation value S_in before correction is different from the command gradation value, the gradation value S_out to be output is calculated by linear interpolation as shown in FIG. In the linear interpolation in the figure, linear interpolation is performed between the corrected gradation values S_out (Sbt, Sct, Sdt) corresponding to the command gradation values (Sb, Sc, Sd). However, the present invention is not limited to this. For example, the correction value H corresponding to the gradation value S_in is calculated by linearly interpolating between the correction values (Hb, Hc, Hd) corresponding to each command gradation value, and the correction value H is calculated based on the calculated correction value H. The corrected gradation value may be calculated as S_in × (1 + H).

  For the C pixel data corresponding to the first to thirty-th column regions of the leading edge printing region, the printer driver uses the first to thirty-th column regions stored in the correction value table for the leading edge printing region. The gradation value correction process is performed based on the correction value corresponding to. For example, for the C pixel data in the first row region of the leading edge printing region, the printer driver is based on the correction values (Hb_1, Hc_1, Hd_1) of the first row region in the correction value table for leading edge printing. Then, gradation value correction processing is performed.

  Similarly, for the C pixel data corresponding to the first to seventh column regions (the 31st to 38th column regions of the entire print region) of the normal print region, the printer driver uses the normal print region. The gradation value correction processing is performed based on the correction values corresponding to the first to seventh row regions stored in the correction value table. However, although there are thousands of row regions in the normal print region, only the correction values corresponding to the seven row regions are stored in the correction value table for the normal print region. Therefore, for the C pixel data in the eighth to fourteenth column regions of the normal print region, the printer driver uses the first to seventh column regions stored in the correction value table for the normal print region. The gradation value correction process is performed based on the correction value corresponding to. As described above, for the row region of the normal print region, the printer driver repeatedly uses the correction values corresponding to the first to seventh row regions for every seven row regions. Since the regular print area has regularity for every seven row areas, it is considered that the density unevenness characteristic is repeated in the same cycle. Therefore, by repeatedly using the correction value in the same cycle, the correction value to be stored The amount of data is reduced.

  Although the number of normal print areas of the correction pattern is 56, the number of the normal print areas of the print image printed by the user is larger than this, reaching several thousand. . A trailing edge printing area composed of 30 row areas is formed on the upstream side of the normal printing area in the transport direction (the trailing edge side of the paper).

  In the trailing edge printing area, similarly to the leading edge printing area, the printer driver stores the C pixel data in the first to thirty-th column areas of the trailing edge printing area in the correction value table for the trailing edge printing area. The gradation value correction processing is performed based on the correction values corresponding to the first to 30th row regions.

  With the above tone value correction processing, a column region that is easily visible darkly is corrected so that the tone value of the C pixel data corresponding to the column region is low. On the other hand, for a column region that is faint and easily visible, correction is performed so that the gradation value of the C pixel data corresponding to the column region becomes high. Note that the above-described tone value correction processing is similarly performed on image data relating to colors other than cyan (C), that is, M, Y, and K image data.

  Next, the printer driver performs halftone processing (S270). Halftone processing is a process of converting each CMYK pixel data indicated by multi-level gradation values on CMYK image data into CMYK pixel data indicated by low-level gradation values that can be expressed by the printer 1. It is.

  In the following, the C image data relating to cyan (C) will be described as a representative example. For example, C pixel data indicating 256 gradation values is converted into 2-bit C pixel data indicating four gradation values by halftone processing. Is converted to The 2-bit C pixel data includes, for example, “no dot formation” (binary value “00”), “small dot formation” (also “10”), “medium dot formation” (also “01 )) And “large dot formation” (also “11”), the dot generation rate of each size is determined according to the gradation value.

  FIG. 25 is an explanatory diagram of a dot generation rate table that defines the correspondence between the gradation value and the dot generation rate. The horizontal axis indicates the gradation value (0 to 255) of the C pixel data before halftone processing, and the vertical axis indicates the dot generation rate (%). Here, the “dot generation rate” means the proportion of pixels in which dots are formed among pixels in a region when a uniform region is reproduced according to a certain gradation value. . The dot generation rate table is stored in advance in the memory of the computer 110.

  As shown in the figure, the correspondence between the gradation value and the dot generation rate is defined for each dot size. That is, in the dot generation rate table of the illustrated example, only the generation rate of the small dots is a positive value in the range of gradation values greater than zero and less than or equal to the first gradation value gr1, and the first gradation value In the range of gradation values greater than gr1 and less than or equal to the second gradation value gr2, only the generation rate of the small dots and the medium dots is a positive value, and the gradation value is larger than the second gradation value gr2. In the range, it is defined that the generation rate of the large dots is a positive value. Therefore, for example, in the pixel in which the gradation value gr larger than the second gradation value gr2 is designated, the probability of being a small dot is 1d (%) and the probability of being a medium dot is 2d (%) as shown in the figure. ), The probability of becoming a large dot is 3d (%), and the probability of no dot is 100-1d-2d-3d (%). That is, the C pixel data corresponding to this pixel has the probabilities of “10”, “01” with the probabilities of 1d (%), 2d (%), 3d (%), and 100-1d-2d-3d (%). , “11”, and “00” are converted into 2-bit data.

  Incidentally, such a halftone process is performed on the C pixel data for which the gradation value correction process (S250) has been executed. Therefore, the generation rate of dots that should be formed in a row region that is easy to see darkly becomes substantially lower by the correction of the gradation value, and conversely, the generation rate of dots that should be formed in a row region that is easy to see lightly On the contrary, the value is generally higher than the correction of the gradation value.

  Next, the printer driver performs rasterization processing (S290). The rasterizing process is a process of changing matrix image data in the order of data to be transferred to the printer 1. The rasterized data is output to the printer 1 as pixel data included in the print data.

  If the printer 1 performs the printing process based on the print data generated in this way, finally, through the change in the generation rate of the dots to be formed in each row area, the image pieces in the row area are changed. The density is corrected and density unevenness of the entire printed image is suppressed.

  In the above description, the number of nozzles and the number of row regions (the number of dot rows) are reduced for the sake of simplification. However, in actuality, the number of nozzles is 180, for example, in the leading edge print region. The number of row regions is 360. However, the processing performed by the correction value setting program, the printer driver, etc. is almost the same.

=== Halftone Processing of the Present Embodiment (S270) ===
<Problems of the above-mentioned halftone processing (S270)>
As described above, the halftone process is performed on the CMYK image data after the gradation value correction process in step S250. Therefore, depending on the correction value associated with the row region and the gradation value of the pixel data, the generation rate of a dot of a certain size among the small, medium, and large dots is a positive value accompanying the gradation value correction process. Can change from zero to zero.

  In other words, it is possible that the dot of a certain size that should have been formed in the row region if it is a gradation value before gradation value correction is not formed at all in the gradation value after gradation value correction. . In that case, there is a possibility that the row region may look like density unevenness because the dot of a certain size is not formed at all in the row region.

  FIG. 26A and FIG. 26B are diagrams for explaining an example of this phenomenon, and are image diagrams in a state where cyan (C) dots are formed on paper. FIG. 26A shows a case of printing based on C image data before gradation value correction, and FIG. 26B shows a case of printing based on C image data after gradation value correction. Each grid in the drawing indicates a unit area (pixel), and each row area is numbered from No. 1 to No. 10. Although the C image data will be described below, the same phenomenon can occur with other color image data.

  Here, for convenience of explanation, it is assumed that the gradation value of the C pixel data before the gradation value correction is a constant value of 29 over all the C pixel data. In addition, the sixth column region in FIG. 26A is associated with a negative correction value having a large absolute value as a correction value for the gradation value correction, and the other column regions have absolute values. It is assumed that a small negative correction value is associated, and as a result, the C pixel data corresponding to the sixth row region is corrected from the 29 to 24 gradation values by the gradation value correction processing. On the other hand, in the C pixel data corresponding to the column regions other than the sixth column region, the description will be made on the assumption that the gradation value is corrected from 29 to 27.

  When dots are formed on the paper based on the C image data before the gradation value correction, since the gradation value is 29 over all the C pixel data, based on the dot generation rate table, As shown in FIG. 27, small dots are formed on paper with a generation rate of 40%, and medium dots are formed with a generation rate of 3%. That is, as shown in FIG. 26A, in any row area, medium dots are formed in the unit area at a ratio of approximately 3 out of 100, while small dots are approximately at a ratio of 40 out of 100 unit areas. Formed. As a result, small dots and medium dots are mixed in each row area, and the configuration of the dots is the same over all row areas, so the formation state of these dots is macroscopically, It looks almost uniform with no density unevenness.

  On the other hand, when dots are formed based on the C image data after the gradation value correction, the C pixel data corresponding to the row area other than the sixth row area is processed by the gradation value correction process. Since the tone value is corrected from 29 to 27, based on the dot generation rate table of FIG. 27, the generation rate of small dots is 40%, and the generation rate of medium dots is 2%. Therefore, as shown in FIG. 26B, small dots and medium dots are mixedly formed in each row region other than the sixth row region, almost the same as before the gradation value correction. However, in the sixth row area, the gradation value is corrected from 29 to 24 by the gradation value correction processing, and therefore, based on the dot generation rate table of FIG. Although slightly reduced to 38%, the medium dot generation rate changes from 3% to 0%. That is, as shown by a thick frame in FIG. 26B, only small dots are formed in the sixth row region, and no medium dots are formed at all. In this case, the sixth row region lacks continuity with other row regions in terms of dot configuration, and as a result, the sixth row region looks like density unevenness. . In other words, there is a possibility that density unevenness is induced in spite of the gradation value correction processing being performed to suppress density unevenness.

  Therefore, in the halftone process of the present embodiment described below, in order to suppress density unevenness that may occur due to such gradation value correction, the generation rate of medium dots is determined by the gradation value correction. It is determined whether or not the positive value changes to zero, and the dot generation rate table to be used is changed based on the result of this determination.

  That is, in the memory of the computer 110 according to the present embodiment, an auxiliary dot generation rate table is also prepared in addition to the regular dot generation rate table (FIG. 25) that is commonly used. Then, when it is determined on the normal dot generation rate table that the medium dot generation rate is changed from a positive value to zero by the gradation value correction, the dot generation rate table to be used is changed to the normal dot generation rate table. The generation rate table is changed to the auxiliary dot generation rate table.

  Here, in this auxiliary dot generation rate table, as will be described later, it is devised so that the generation rate of medium dots becomes a positive value even for the gradation value after the gradation value correction. Is preset. Therefore, the generation rate of the medium dots in the row area is maintained at a positive value even in the gradation value after the gradation value correction, and medium dots are formed in the row area. The continuity of the constituent dots is generally maintained. As a result, it is effectively prevented that the row region looks like density unevenness.

<Halftone processing of this embodiment>
FIG. 28 is a flowchart of halftone processing according to this embodiment. Here, the process for the C image data of the CMYK image data will be described, but the other M, Y, K image data are processed in the same manner.

  First, in step S271, the printer driver acquires C image data after gradation value correction processing. In the next step S272, one C pixel data is designated as C pixel data to be processed from the C image data, and a gradation value of the C pixel data is acquired. This gradation value is, of course, the gradation value after gradation value correction.

  If so, the regular dot generation rate table is referred to based on the gradation value, and it is determined whether or not the generation rate of the medium dot is changed from the positive value to zero by the gradation value correction (S273).

  This determination is performed as follows, for example. First, the printer driver refers to the regular dot generation rate table in FIG. 29A to check whether the generation rate of medium dots corresponding to the gradation value gra of the C pixel data is zero. It is also checked whether the medium dot generation rate corresponding to the gradation value grb before the value correction is a positive value. Then, as shown in FIG. 29A, when both of them are applicable, it is determined that “the generation rate of medium dots is changed from a positive value to zero by the gradation value correction” while FIG. As shown in 29B, if it does not fall into at least one of the two, it is determined that the medium dot generation rate does not change from a positive value to zero by the gradation value correction. Incidentally, the gradation value grb before gradation value correction is obtained by obtaining the correction value H of the column region to which this C pixel data belongs from the correction value table, and adding the value 1 to the correction value H to obtain the C pixel data. Is obtained by dividing the gradation value gra of.

  If the result of the determination is that “the generation rate of medium dots does not change from a positive value to zero by the gradation value correction” (No in S273), the process proceeds to step S274b, and the printer driver The generation rate corresponding to the gradation value gra is acquired for each of the small, medium and large dots based on the regular dot generation rate table as it is.

  On the other hand, if it is determined in step S273 that "the generation rate of medium dots is changed from a positive value to zero by the gradation value correction" (Yes in S273), the process proceeds to step S274a, and the auxiliary dot is set. With reference to the generation rate table (FIG. 30B), the generation rate corresponding to the gradation value gra is acquired for each of the small, medium and large dots. In other words, when the generation rate is acquired based on the regular dot generation rate table, medium dots that should be formed before gradation value correction are not formed. In this case, an auxiliary dot generation rate table is used. Refer to it.

  30A and 30B are diagrams showing an auxiliary dot generation rate table in comparison with the normal dot generation rate table. As can be seen from these figures, in the auxiliary dot generation rate table of FIG. 30B, the gradation value (hereinafter referred to as the first gradation value gr1) in which the generation rate of the medium dots changes from zero to a positive value. Is set to a value smaller than the regular dot generation rate table of FIG. 30A. For example, the first tone value gr1 is 25 in the regular dot generation rate table of FIG. 30A, but is 19 in the auxiliary dot generation rate table of FIG. 30B. Therefore, as shown in FIG. 30A, even when the generation rate of medium dots corresponding to the gradation value grad (for example, 24) after gradation value correction in the regular dot generation rate table is zero, FIG. According to the auxiliary dot generation rate table shown in FIG. 2, the medium dot generation rate is maintained at a positive value.

  Incidentally, the deviation Δgr1 between the first gradation value gr1 of the auxiliary dot generation rate table and the first gradation value gr1 of the normal dot generation rate table can be corrected by the gradation value correction process (S250). The correction value of the gradation value (the difference between the gradation values before and after the gradation value correction (= grb−gra) is set to a larger value. For example, here, as a result of the sample investigation, the correction amount is set. It has been found that the maximum value of 5 is 5. Therefore, the Δgr1 is set to 6. Therefore, in the auxiliary dot generation rate table, the gradation value grad after the gradation value correction always includes a medium dot. A positive value generation rate is associated with.

  When the generation rate is obtained for each of the small, medium, and large dots through any of the branching steps of step S274a and step S274b, the printer driver proceeds to step S275, and the C pixel is obtained based on the obtained generation rates. The gradation value of data is converted into 2-bit data. That is, the gradation value of the C pixel data is determined based on the probability of each generation rate, 2-bit data “10” indicating “small dot formation” and 2-bit data “01” indicating “medium dot formation”. , And 2-bit data “11” indicating “large dot formation” and 2-bit data “00” indicating “no dot formation”.

  If so, the printer driver proceeds to step S276 to determine whether or not halftone processing has been completed for all C pixel data, and if not, sets the processing target to an unprocessed C. The pixel data is changed (S277), and the process returns to step S272 described above. On the other hand, if the halftone process has been completed for all the C pixel data in step S276, the halftone process for the C image data is completed.

  The halftone processing according to the present embodiment has been described above. Here, the supplementary dot generation rate table described above will be slightly supplemented.

  The auxiliary dot generation rate table shown in FIG. 30B defines the correspondence between gradation values and dot generation rates as follows, as in the normal dot generation rate table of FIG. 30A. In the range of gradation values greater than zero and less than or equal to the first gradation value gr1, only the small dot generation rate is a positive value, and is greater than the first gradation value gr1 and less than or equal to the second gradation value gr2. In the gradation value range, only the generation rate of the small dot and the medium dot is a positive value, and in the gradation value range larger than the second gradation value gr2, the generation rate of the large dot is a positive value. It is.

  However, since the first gradation value gr1 is set to a value smaller than the first gradation value gr1 of the regular dot generation rate table, the first floor of the auxiliary dot generation rate table is accordingly accompanied. In the gradation values after the tone value gr1, the medium dot generation rate is higher than the normal dot generation rate table. Therefore, in the auxiliary dot generation rate table as it is, the macroscopic density when printed on paper is increased by the increase in the generation rate of medium dots, but in the auxiliary dot generation rate table of FIG. 30B, The generation rate of small dots is lowered from the normal dot generation rate by the increase in the generation rate of medium dots. Therefore, even when dots are formed on the paper based on the auxiliary dot generation rate table, the density of the darkness corresponding to the gradation value is expressed macroscopically.

<Example of Dither Method for Halftone Processing of this Embodiment>
For example, a dither method, a γ correction method, an error diffusion method, or the like is used as a method for performing the halftone process of the present embodiment.

  FIG. 31 is a flowchart when the halftone process of this embodiment is performed by the dither method. Here, only the C image data will be described here, but other M, Y, K image data are processed in the same manner.

  First, in step S501, the printer driver acquires C image data after gradation value correction processing. In the next step S502, one C pixel data is designated as C pixel data to be processed from the C image data, and a gradation value of the C pixel data is acquired.

  Then, the process proceeds to steps S503 and S504, and a normal dot generation rate table is referred to based on the gradation value, and whether or not the generation rate of medium dots changes from a positive value to zero by the gradation value correction. However, in this dither method, the following processing is performed using level data instead of the generation rate.

  32A and 32B are diagrams of the regular dot generation rate table for explaining the level data. The difference from the dot generation rate table of FIG. 29A described above is that level data is set on the right vertical axis in correspondence with the dot generation rate (%) set on the left vertical axis. The rest is the same.

  This level data refers to data obtained by uniformly assigning 0 to 100% generation rate to 256 levels of 0 to 255. For example, zero level data corresponds to 0% generation rate. In addition, the level data of 255 corresponds to the generation rate of 100%. As shown in FIG. 32A, the dot generation rate table defines level data LVS, LVM, and LVL for small, medium, and large dots corresponding to the generation rates of small, medium, and large dots.

  When such level data is used, the above-described “determination as to whether or not the generation rate of medium dots changes from a positive value to zero by gradation value correction” is performed as follows. . First, with reference to the regular dot generation rate table of FIG. 32B, it is checked whether the level data LVM of the medium dot corresponding to the gradation value gra is zero, and further, the gradation value before gradation value correction is performed. It is also checked whether the medium dot level data LVM ′ corresponding to grb is a positive value. If both of these conditions apply, the determination that “the generation rate of medium dots changes from a positive value to zero by the gradation value correction” is made, while at least one of the cases is not satisfied Is determined that “the generation rate of medium dots does not change from a positive value to zero by the gradation value correction”.

  If the result of the determination is “the medium dot generation rate does not change from a positive value to zero” (No in S504), the process proceeds to step S505b, and the normal dot generation rate table as it is. , Each level data LVS, LVM, LVL of small, medium and large dots corresponding to the gradation value gra is acquired.

  On the other hand, if it is determined that “the generation rate of the medium dots changes from a positive value to zero” (Yes in S504), the process proceeds to step S505a, and the auxiliary dot generation rate table (FIG. 33B) is referred to. Then, small, medium and large dot level data LVS, LVM and LVL corresponding to the gradation value are acquired. That is, in the normal dot generation rate table, the medium dot level data LVM becomes zero, and the medium dot that should be formed before the gradation value correction is not formed. The dot generation rate table is referred to.

  FIG. 33A and FIG. 33B are comparative diagrams showing the auxiliary dot generation rate table in comparison with the normal dot generation rate table. As can be seen from these comparisons, in the auxiliary dot generation rate table, the gradation value (first gradation value gr1) at which the medium dot level data LVM changes from zero to a positive value is a normal value. It is set to a smaller value than in the dot generation rate table. Therefore, as shown in FIG. 33A, even when the medium dot level data LVM corresponding to the gradation value gra after gradation value correction in the regular dot generation rate table becomes zero, the auxiliary dot According to the generation rate table, as shown in FIG. 33B, the medium dot level data LVM is maintained at a positive value.

  Then, when the level data LVS, LVM, and LVL are acquired for each of the small, medium, and large dots through any of the branching steps of step S505a and step S505b, based on the acquired level data LVS, LVM, and LVL, The subsequent steps S506 to S513 are sequentially executed to convert the C image data into 2-bit data.

  First, in step S506, it is determined whether or not the large dot level data LVL is greater than or equal to a threshold value THL. That is, dot on / off determination is performed by the dither method. The threshold value THL is set to a different value for each pixel block of a so-called dither matrix. In the present embodiment, a matrix in which values from 1 to 255 appear almost evenly in a 16 × 16 square pixel block is used.

  FIG. 34 is a diagram showing a state of dot on / off determination by the dither method. For the sake of illustration, FIG. 34 shows only some C pixel data. First, as shown in the figure, the level data LVL of each C pixel data is compared with the threshold value THL of the pixel block on the dither matrix corresponding to the C pixel data. When the level data LVL is equal to or greater than the threshold value THL, the dot is turned on, and when it is less than the threshold value THL, the dot is turned off. In the figure, shaded C pixel data is C pixel data for turning on a dot. That is, in step S506, if the level data LVL is greater than or equal to the threshold value THL, the process proceeds to step S507, and otherwise, the process proceeds to step S508. When the process proceeds to step S507, the printer driver records the 2-bit data “11” indicating a large dot in association with the C pixel data to be processed, and the process proceeds to step S513. In step S513, it is determined whether or not the processing has been completed for all the C pixel data. If the processing has been completed, the halftone processing is ended. If the processing has not been completed, the processing target is determined. The process proceeds to unprocessed C pixel data (S514), and the process returns to step S502.

  On the other hand, if the process proceeds to step S508, the medium dot level data LVM and the threshold value THM are compared to determine whether the medium dot is on or off. The on / off determination method is the same as that for large dots, but the threshold value THM used for determination is set to a value different from the threshold value THL for large dots as shown below. That is, when ON / OFF determination is performed using the same dither matrix for large dots and medium dots, the pixel blocks where the dots are likely to be turned on coincide with each other. That is, when a large dot is turned off, there is a high possibility that a medium dot is also turned off. As a result, the medium dot generation rate may be lower than the desired generation rate. In order to avoid such a phenomenon, here, the dither matrix is changed for both. In other words, the pixel blocks that are likely to be turned on are changed between large dots and medium dots, thereby ensuring that each is appropriately formed.

  FIG. 35A is a diagram illustrating a dither matrix used for large dot determination, and FIG. 35B is a diagram illustrating a dither matrix used for medium dot determination. In this example, the dither matrix TM shown in FIG. 35A is used for large dots, and the dither matrix UM shown in FIG. 35B is used for medium dots. . Here, as described above, a 16 × 16 matrix is used, but in FIGS. 35A and 35B, a 4 × 4 matrix is shown for convenience of illustration. Note that dither matrices that are completely different for large dots and medium dots may be used.

  In step S508, if the medium dot level data LVM is equal to or greater than the medium dot threshold value THM, it is determined that the medium dot should be turned on, and the process proceeds to step S509. Otherwise, step S510 is performed. Proceed to If the process proceeds to step S509, the printer driver records the C pixel data to be processed in association with the 2-bit data “01” indicating a medium dot, and the process proceeds to step S513 described above. .

  On the other hand, when the process proceeds to step S510, the small dot level data LVS and the threshold value THS are compared in this step S510 to determine whether small dots are on or off. If the small dot level data LVS is equal to or larger than the small dot threshold THS, the process proceeds to step S511. Otherwise, the process proceeds to step S512. If the process proceeds to step S511, 2-bit data “10” indicating a small dot is recorded in association with the C pixel data to be processed, and the process proceeds to step S513 described above. On the other hand, if the process proceeds to step S512, the printer driver records the 2-bit data “00” indicating no dot in association with the C pixel data to be processed, and the process proceeds to step S513 described above.

=== Other Embodiments ===
The above-described embodiment is mainly described for the printing system 100 including the printer 1, but it goes without saying that the disclosure includes a printing method and the like.
Further, the printer 1 and the like as one embodiment have been described, but the above-described embodiment is for facilitating understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About Printer 1>
In the above-described embodiment, the printer 1 has been described. However, the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, liquid vaporization apparatus, organic EL manufacturing apparatus (particularly polymer EL manufacturing apparatus), display manufacturing apparatus, film formation The same technique as that of the present embodiment may be applied to various recording apparatuses to which an ink jet technique is applied such as an apparatus and a DNA chip manufacturing apparatus.

<About nozzle>
In the above-described embodiment, ink is ejected using a piezo element, but the method of ejecting ink is not limited to this. For example, other methods such as a method of generating bubbles in the nozzle by heat may be used.

<About the moving direction of the head 41>
In the above-described embodiment, it is not described whether the ink is ejected when the head 41 moves in the reciprocating direction. However, the ink is ejected only in the forward path, only in the return path, or both in the reciprocal direction. May be.

<Ink colors used for printing>
In the above-described embodiment, multicolor printing in which four inks of cyan (C), magenta (M), yellow (Y), and black (K) are ejected onto paper to form dots has been described as an example. The ink color is not limited to this. For example, in addition to these ink colors, ink such as light cyan (light cyan, LC) and light magenta (light magenta, LM) may be used.

  Conversely, monochrome printing may be performed using only one of the four ink colors.

<About the certain size>
In the above-described embodiment, the case of medium dots as the certain size has been described as an example. That is, the case where the dot generation rate table is changed based on whether or not the generation rate of medium dots is changed from a positive value to zero by gradation value correction is illustrated, but the present invention is not limited to this. . For example, the dot generation rate table may be changed based on whether or not the generation rate of large dots changes from a positive value to zero by gradation value correction. However, the second gradation value gr2 at which the generation rate of large dots changes from zero to a positive value is generally a gradation value in a so-called halftone region in which density unevenness is easily visible (for example, a gradation value range of 0 to 77). ) Is not as effective as the above-described medium dot example.

1 is an explanatory diagram of a configuration of a printing system 100. FIG. 1 is a block diagram of an overall configuration of a printer 1. FIG. FIG. 3A is a schematic diagram of the overall configuration of the printer 1, and FIG. 3B is a cross-sectional view of the overall configuration of the printer 1. 4 is an explanatory diagram of an arrangement of nozzles on a lower surface of a head 41. FIG. It is explanatory drawing of the drive circuit 220 for driving the said piezo element. 4 is a timing chart of an original drive signal ODRV, a print signal PRT (i), and an actual drive signal DRV (i) showing the operation of the original drive signal generator 221. 5A is a longitudinal sectional view of the scanner 150, and FIG. 5B is a top view of the scanner 150 with the upper cover 151 removed. It is a flowchart of the operation | movement at the time of printing. 7A and 7B are explanatory diagrams of normal printing. It is explanatory drawing of front end printing and rear end printing. FIG. 9A is an explanatory diagram of a state when dots are ideally formed, FIG. 9B is an explanatory diagram of the influence of variations in nozzle processing accuracy, and FIG. 9C is obtained by the printing method of the present embodiment. It is explanatory drawing of a mode when a dot is formed. FIG. 6 is a flowchart of correction value acquisition processing performed after manufacturing of the printer 1. It is explanatory drawing of a test pattern. It is explanatory drawing of the pattern for a correction | amendment. It is explanatory drawing of the reading range of the pattern for cyan correction. 14A is an explanatory diagram of image data at the time of tilt detection, FIG. 14B is an explanatory diagram of detection of the position of the upper ruled line, and FIG. 14C is an explanatory diagram of image data after the rotation processing. 15A is an explanatory diagram of image data at the time of trimming, FIG. 15B is an explanatory diagram of a trimming position at the upper ruled line, and FIG. 15C is an explanatory diagram of a trimming position at the lower ruled line. It is explanatory drawing of resolution conversion. FIG. 17A is an explanatory diagram of image data at the time of detection of the left ruled line, FIG. 17B is an explanatory diagram of detection of the position of the left ruled line, and FIG. 17C is a band-like shape having a density of 30% in the first row region. It is explanatory drawing of the measurement range of the density of a pattern. It is the measurement value table which put together the measurement result of the density | concentration of five types of strip | belt-shaped patterns of cyan. It is a graph of the measured value of the strip | belt-shaped pattern of density 30%, density 40%, and density 50% of cyan. 20A is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region A, and FIG. 20B is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region B. is there. It is explanatory drawing of the correction value table of cyan. It is a flowchart of the process performed under the user. It is a flowchart of a print data generation process. It is explanatory drawing of the density correction process of the nth row | line area | region of cyan. It is explanatory drawing of a dot production rate table. FIG. 26A and FIG. 26B are diagrams for explaining an example of a phenomenon in which density unevenness occurs due to gradation value correction, and each is an image diagram in a state where cyan (C) dots are formed on paper. . It is a figure which expands and shows a part of dot generation rate table of FIG. It is a flowchart of the halftone process which concerns on this embodiment. FIG. 29A and FIG. 29B are explanatory diagrams of a method for determining whether or not the medium dot generation rate changes from a positive value to zero by the gradation value correction. FIG. 30A is a normal dot generation rate table, and FIG. 30B is an auxiliary dot generation rate table. It is a flowchart in case the halftone process of this embodiment is performed by the dither method. 32A and 32B are diagrams of the regular dot generation rate table for explaining the level data. FIG. 33A is a normal dot generation rate table, and FIG. 33B is an auxiliary dot generation rate table. It is a figure which shows the mode of the dot ON / OFF determination by a dither method. FIG. 35A is a diagram illustrating a dither matrix used for large dot determination, and FIG. 35B is a diagram illustrating a dither matrix used for medium dot determination.

Explanation of symbols

1 printer, 5 manuscripts,
20 transport unit, 21 paper feed roller, 22 transport motor, 23 transport roller,
24 platen, 25 paper discharge roller,
30 Carriage unit, 31 Carriage, 32 Carriage motor,
40 head units, 41 heads,
50 detector groups, 51, linear encoder, 52, rotary encoder,
53 Paper detection sensor, 54 Optical sensor,
60 controller, 61 interface unit, 62 CPU, 63 memory,
64 unit control circuit,
100 printing system, 110 computer, 120 display device,
130 input device, 140 recording / reproducing device, 150 scanner,
151 Upper lid, 152 Document platen glass, 153 Reading carriage, 154 Guide member,
155 Movement mechanism, 157 exposure lamp, 158 line sensor, 159 optical system

Claims (11)

The dot generation rate corresponding to the density gradation value of the image data is obtained by referring to correspondence information that defines the correspondence between the density gradation value and the dot generation rate for dots of a plurality of sizes. A printing method for printing an image by forming the dots on a medium based on the generation rate,
When correcting the gradation value of the image data based on a predetermined density correction value, whether or not the generation rate of a dot of a certain size among the plurality of sizes is changed from a positive value to zero by the correction. A step of determining whether or not
Changing the correspondence information based on a result of the determination. A printing method comprising: The printing method according to claim 1,
The plurality of size dots are small dots, medium dots larger than the small dots, and large dots larger than the medium dots,
The printing method according to claim 1, wherein the correspondence information is a dot generation rate table that defines a correspondence relationship between the gradation value and the dot generation rate for each size. The printing method according to claim 2,
In the dot generation rate table,
In a range of gradation values greater than zero and less than or equal to the first gradation value, only the small dot generation rate is a positive value;
In the range of gradation values greater than the first gradation value and less than or equal to the second gradation value, only the generation rate of the small dots and the medium dots is a positive value;
The printing method is characterized in that the generation rate of the large dots is defined as a positive value in a range of gradation values larger than the second gradation value. The printing method according to claim 3,
The printing method according to claim 1, wherein the dot of a certain size is the medium dot. The printing method according to claim 4,
As the dot generation rate table, an auxiliary dot generation rate used in place of the regular dot generation rate table when the determination result is zero, in addition to the regular dot generation rate table that is used regularly. A table is prepared,
In the auxiliary dot generation rate table, the first gradation value is set to a smaller value than in the regular dot generation rate table. In the printing method in any one of Claims 1 thru | or 5,
The image is printed by repeating an ink ejection operation for ejecting ink from the nozzle while moving the nozzle in the movement direction, and a conveyance operation for conveying the medium in a conveyance direction that intersects the movement direction.
The gradation value of the image data is set for each unit region adjacent to the moving direction and adjacent to the transport direction,
The printing method according to claim 1, wherein the determination is performed for each unit area. The printing method according to claim 6, wherein
The image is divided with respect to the transport direction in row area units composed of a plurality of the unit areas adjacent in the moving direction,
The printing method, wherein the correction value is set for each row region. The printing method according to claim 7,
The printing method, wherein the correction value is set based on a reading value of density read for each row region from a test pattern printed at a predetermined density. The printing method according to any one of claims 1 to 8,
When the generation rate is α% in a plurality of unit regions, the dots are formed in α% unit regions of the plurality of unit regions. In the printing method in any one of Claims 6 thru | or 9,
The image is composed of a plurality of color dots,
The image data has the gradation value for each color,
The correspondence information is prepared for each color,
A printing method, wherein, based on correspondence information of the same color, regulation is performed so that two or more dots are not overlapped in the same unit area. The dot generation rate corresponding to the density gradation value of the image data is obtained by referring to correspondence information that defines the correspondence between the density gradation value and the dot generation rate for dots of a plurality of sizes. A printing method for printing an image by forming the dots on a medium based on the generation rate,
When correcting the gradation value of the image data based on a predetermined density correction value, whether or not the generation rate of a dot of a certain size among the plurality of sizes is changed from a positive value to zero by the correction. A step of determining whether or not
Changing the correspondence information based on the result of the determination, and
The plurality of size dots are small dots, medium dots larger than the small dots, and large dots larger than the medium dots, and the correspondence information includes the gradation value and the dot generation rate. It is a dot generation rate table that defines the correspondence for each size,
In the dot generation rate table, in the range of gradation values greater than zero and less than or equal to the first gradation value, only the small dot generation rate is positive and greater than the first gradation value. In the range of gradation values equal to or lower than the second gradation value, only the generation rate of the small dots and the medium dots is positive, and in the range of gradation values larger than the second gradation value, It is specified that the generation rate of large dots is a positive value,
The dot of the certain size is the medium dot,
As the dot generation rate table, an auxiliary dot generation rate used in place of the regular dot generation rate table when the determination result is zero, in addition to the regular dot generation rate table that is used regularly. A table is prepared, and in the auxiliary dot generation rate table, the first gradation value is set to a smaller value than in the case of the regular dot generation rate table,
The image is printed by repeating an ink ejection operation for ejecting ink from the nozzle while moving the nozzle in the movement direction, and a conveyance operation for conveying the medium in a conveyance direction that intersects the movement direction. The gradation value of data is set for each unit region adjacent to the moving direction and adjacent to the transport direction, and the determination is performed for each unit region.
The image is divided in a row region unit composed of a plurality of unit regions adjacent in the moving direction, and is divided with respect to the transport direction, and the correction value is set for each row region,
The correction value is set based on a density reading value read for each row region from a test pattern printed at a predetermined density,
When the generation rate is α% in a plurality of unit regions, the dots are formed for α% unit regions of the plurality of unit regions,
The image is composed of dots of a plurality of colors, the image data has the gradation value for each color, the correspondence information is prepared for each color, and is based on the correspondence information of the same color The printing method is characterized in that two or more dots are not overlapped in the same unit area.